The unique oxygen sensing capacity of the sickle red cell defines sickle cell disease (SCD) pathology resulting from the polymerization of sickle hemoglobin under low partial oxygen pressure (PO2). Our long term goal is to understand how intermittent hypoxia changes the red cell membrane and its interactions with vascular endothelium (E.C.). We hypothesize a novel chain of events in which intermittent hypoxia will generate lysophosphatidic acid (LPA), a powerful lipid mediator, exposes phosphatidyl serine (PS) on the red surface, and depletes plasma gelsolin levels, the buffer protein for LPA. We pose that nitric oxide (NO) and related compounds, generated by E.C. under hypoxia will affect this process depending on the hemoglobin concentration and type (HbS, or HbF). Increased levels of the inflammatory mediator secretory phospholipase A2 (sPLA2) in SCD will further exacerbate this process which will ultimately lead to vascular drainage. To address these aspects of RBC-E.C. interaction, we have developed the following specific aims: I. To investigate the effect of intermittent hypoxia on sickle red cells. II. To investigate intermittent hypoxia on red cell-endothelial interaction, and III. To evaluate factors of intermittent hypoxia in sickle cell patients and murine models of sickle cell disease. To accomplish these goals, we will use a multidisciplinary approach using biochemistry and cell biology techniques to study RBC and E.C. under well-defined conditions of intermittent hypoxia in vitro, in a unique incubation system, separately or together. We will measure the generation of LPA in vitro and define its role, determine the LPA buffering capacity of the plasma actin-binding protein gelsolin, and define the role for E.C. derived NO and its derivatives. We will relate the data of in vitro studies to in vivo findings of LPA, gelsolin and NO footprints in SCD patients with vasoocclusive crisis, stroke and acute chest syndrome as well as our murine model for SCD. Together, our results may indicate novel treatment regiments in the management of SCD.